This application claims the benefit of United Kingdom Patent Application No. GB0807310.8, filed on Apr. 22, 2008, which hereby is incorporated by reference in its entirety.
In the field of oil and gas exploration and production, it is common to provide ring members on longitudinal tools, bodies, tubulars or mandrels. Typically, ring members are sized to be slipped on to the tubular or mandrel and moved longitudinally into the desired position where they are secured to the body. A typical function of a ring member is to prevent or restrict axial movement of an adjacent component on the body.
One particular application in which ring members are required is in the construction of swellable packers. A swellable packer includes a mantle of swellable elastomeric material formed around a tubular body. The swellable elastomer can be selected to expand by increasing in volume on exposure to at least one triggering fluid, which may be a hydrocarbon fluid or an aqueous fluid. The design dimensions and swelling characteristics are selected such that the swellable mantle expands to create a fluid seal in the annulus, thereby isolating one wellbore section from another. Swellable packers have several advantages over conventional packers, including passive actuation, simplicity of construction, and robustness in long term isolation applications. Examples of swellable packers are described in GB 2411918.
It will often be desirable to provide a ring member on either side of the swellable mantle. The ring member is secured to the main body of the tool, and is upstanding from the body. The ring member restricts or prevents axial movement of the swellable mantle on the body. It also provides stand-off protection for the swellable mantle and/or adjacent parts of the tool string during run-in. The ring member also provides an annular abutment surface for the swellable mantle which assists in reducing or preventing extrusion of the elastomer due to fluid pressure or pulling, i.e., downward, forces on the tubular. This improves the integrity of the seal provided by the packer.
Various methods have been used to secure retaining elements and gauge rings to the body. For example, a retaining element may be fixed by welding. In another technique, bolts are provided in threaded bores in the retaining element, and are screwed radially into the body, as described in co-pending International patent application number PCT/GB2007/004445 (published as WO2008/062178).
WO 2006/115417 discloses an alternative system which includes a ring fastener provided with protrusions on an inner surface which correspond to recesses in a body. The ring fastener is plastically deformed by radial shrinking of an outer sleeve so that the protrusions engage the recesses.
Although the system of WO 2006/115417 provides a convenient means for locating a cylinder on a base pipe, the assembly is limited in its resistance to axial forces. For example, during run-in, the outer sleeve may encounter an obstacle which imparts an impulse or tensile force that is large enough to overcome the frictional contact between the base pipe and the fastener. This can result in axial displacement of the sleeve on the body. If the outer sleeve is also required to function as a gauge ring and/or is required to provide stand-off to the base pipe during run-in, the problem is exacerbated. Similar difficulties may apply during use of the apparatus. For example, if the outer sleeve is part of a packer assembly or anchor which couples a tubular to the inner surface of an outer casing or an openhole, a downward weight or pulling force on the tubular is opposed by the outer sleeve, which may be sufficient to overcome the frictional force between the base pipe and the fastener. In addition, the ring fastener of WO 2006/115417 is only suitable for coupling to a body that is provided with recesses in its outer surface.
It is one object of an aspect of the invention to provide a ring member—which may be a gauge ring or a retaining member—for a downhole apparatus which overcomes the deficiencies of the prior art ring members. It is a further aim of the invention to provide an alternative ring member to those proposed in the prior art.
It is another object of an aspect of the invention to provide an assembly of a body and a ring member which has a greater resistance to axial forces and greater structural integrity when compared with prior art assemblies.
It is a further aim of the invention to provide a retaining element which may be used with standard equipment, such as American Petroleum Institute (API) tubular sections and couplings.
Additional aims and objects of the invention will become apparent from the following description.